The present invention relates generally to optical communications, and more particularly, to 802.3av compliant method using small timescale bandwidth assignment for increased optical network unit ONU downstream energy efficiency.
Energy efficient networking has become a key requirement in recent years. The main factors contributing to this need are the reduction of the global carbon footprint but also the reduction of network operational expenditures (OPEX). Moreover, regulators worldwide are beginning to mandate compliance with specific energy consumption figures. For these reasons, novel technological solutions are being sought to minimize energy consumption at various layers, ranging from the physical layer up to the higher ones. Although Passive Optical Networks (PON) are inherently more energy-efficient than other types of access networks due to their use of a passive network infrastructure as shown in FIG. 1, which features a power splitter (300), it is still desirable to cut down energy consumption as much as possible. In fact, the major energy consumption contributors in a PON are the Optical Network Units (ONUs), e.g. ONU i (400) in FIG. 1, located at the customer side. Although a single ONU consumes roughly the same power as an Optical Line Terminal (OLT) (100) port, the sharing of the latter by a multitude of ONUs (typically 16 to 64) implies that major savings per user can be obtained by seeking efficiency at the ONU side. Furthermore, significant reductions in the energy consumed by ONUs are beneficial in case of emergency situations, whereby ONUs would be required to operate in battery mode. The most prominent way of achieving this is to exploit information from the Medium Access Control (MAC) layer to by selectively setting ONU components to “sleep” mode whenever they are not required to operate. For example, the ONU transmitter (Tx) (401) or receiver (Rx) (402) in FIG. 1 can be set to sleep mode whenever the ONU is not scheduled to transmit in the upstream direction or receive in the downstream. At the same time, with the IEEE standard 802.3av for 10G-EPON published recently, an important requirement is to achieve the aforementioned energy-efficient operation without altering the protocol itself, since vendors have already invested in standard-compliant equipment development. Moreover, it is crucial that quality of service (QoS) is compromised as little as possible due to the energy-efficient operation. In fact, the upstream direction case is straightforward since the OLT informs the ONU via GATE Multi Point Control Protocol (MPCP) frames about the upstream timeslots during which it can transmit. Accordingly, the ONU can set its Tx (401) to sleep mode during the rest of the time. For the downstream direction, a similar approach cannot be followed since in general the ONU has to inspect all frames broadcast by the OLT and keep the ones with its own destination address.
A fixed bandwidth allocation (FBA) scheme has been proposed by others to achieve ONU downstream energy efficiency. FIG. 2 shows en example of FBA operation. Downstream transmission is split in scheduling cycles of fixed duration. During each cycle the OLT transmits data to each ONU for a fixed number of timeslots. Let Δk(i) denote the time between the end of downstream transmission to ONU i in cycle k−1 and the beginning of the one in cycle k and Ek (i) the duration of this transmission. In FBA, both Δk(i) and Ek (i) are fixed for all i and k. From the energy efficiency perspective FBA is very effective. Since downstream bandwidth allocation is performed in regular intervals, known in advance to the ONUs, the latter can easily turn their Rx to sleep mode exactly when this is needed. This is indicated in FIG. 2 by the ONU Rx alternating between the awake (‘A’) and asleep (‘S’) mode. The white-colored intervals indicated the requirement for the ONU to switch between states. The latter must be taken into account by the ONU when calculating its next wake-up instant.
The main downside of the previously proposed FBA scheme (FIG. 2) is that it cannot adapt to bursty traffic and does not provide statistical multiplexing among ONUs. In other words, depending on the loading conditions it can either lead to excessive bandwidth waste or delay.
An alternative scheme proposed by others does not use a fixed downstream cycle duration. The exact duration is determined dynamically by the data in the downstream ONU queues and the scheme used for downstream grant sizing. This scheme aims at improving downstream energy efficiency by ensuring that the OLT will never use a downstream scheduling cycle shorter than a given value each time. This value for cycle k is determined for ONU i as ρ·Δk−1(i), where ρ is a system parameter, known to the OLT and all ONUs. Each ONU therefore has to constantly monitor Δk (i) and accordingly set its Rx to sleep mode for a duration equal to ρ·Δk(i) in the next cycle. The OLT on the other hand has to take care not to schedule the next transmission for the ONU sooner than ρ·Δk(i) (it can though be scheduled later than that depending on the traffic of other ONUs). In the next cycle, a new interval Δk+1(i) will be decided based on the data in the rest of the ONUs' queues. In addition, it is crucial that the OLT transmits downstream GATE messages to an ONU only after the transmission of data; otherwise it would be impossible for the ONU to go to sleep without missing some grants.
An example of the alternative scheme of is shown in FIG. 3. This scheme maintains a certain degree of dynamicity, since both Δk(i) and Ek(i) are decided during every cycle. However, its performance is compromised due to the requirement for a minimum cycle time each time. Therefore there is a heavy trade-off between system utilization/delay performance and energy-efficiency. It is probable, depending on the actual traffic patterns, to have either early or late wake ups. In the former case (cycle k+1 in FIG. 3), ρ·Δk(1)<Δk+1(1), resulting in an underestimation of the upcoming cycle and reducing the energy efficiency benefits. In the latter (cycle k+2 in FIG. 3) the upcoming cycle would need to be shorter (given the actual traffic) but the OLT is detained by the ρ·Δk+1(1) function. Therefore, although the selection of the ρ parameter is extremely crucial, the scheme's performance is affected by both the overall network load as well as the exact traffic patterns, rendering the control of QoS versus energy-efficiency trade-off very difficult.
Accordingly, there is a need for solving the problem of ONU-side energy efficient downstream operation with a method that provides a better energy-efficiency/QoS trade-off.